Is there any Constitutional precedent for the claim that it is or is not within the rights or duties of the office of the President of the United States or of Congress to grant, to deny, or to suspend military aid, including any financial aid that may be used in part on military operations?
Clearly I do not mean that the President and Congress jointly have no power to deliver aid, to form alliances, or to reinforce and engage in military actions in cooperation with the allies of the United States during a time of declared war--certainly those activities are within the purview of the Constitutional charter of those bodies. I refer instead to the arbitrary disbursal of aid to foreign countries by the US when the US is not actively engaged in war against mutual enemies of said countries.
Congress has power to declare war, while the President is designated as the commander in chief of the military and may engage in treaties with the consent of two thirds of the senate. No explicit mention justifying foreign aid outside of these bounds seems to have been made or intended by the writers of the Constitution.
According to the Founding Fathers, a key to the United States' sovereignty and security is the strict avoidance of "permanent/entangling alliances" and of over-involvement in foreign sympathies and antagonisms. To engage in any sort of foreign aid (as has become routine for the past many years and presidents) that is not directly tied to US security seems directly contrary to this doctrine, and unsupported Constitutionally.
From General Washington:
The great rule of conduct for us, in regard to foreign nations, is in extending our commercial relations, to have with them as little political connection as possible. Europe has a set of primary interests, which to us have none, or a very remote relation. Hence she must be engaged in frequent controversies the causes of which are essentially foreign to our concerns. Hence, therefore, it must be unwise in us to implicate ourselves, by artificial ties, in the ordinary vicissitudes of her politics, or the ordinary combinations and collisions of her friendships or enmities ... it is our true policy to steer clear of permanent alliances with any portion of the foreign world; so far, I mean, as we are now at liberty to do it; for let me not be understood as capable of patronizing infidelity to existing engagements. (George Washington's Farewell Address, emphasis added)
Thus it would seem that we have no business lending aid or picking sides in foreign conflicts except as those conflicts directly affect the safety of American citizens.
The Constitution itself seems to make the designation of optative military aid on the part of a US government body to a foreign country either forbidden implicitly by the ninth and tenth amendments restricting the functions of government to those explicitly defined, or rather in a Constitutional limbo between Congress and the President, but in any case allowable only as clearly defending US national interests, with the following important and clear restriction:
Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort. (Article III, Section 3 of the U.S. Constitution)
Hence, where is the Constitutional justification for any claim that it is within the rights of a US government body to dispense, suspend, or discontinue foreign aid generally, and especially when the US has not declared war?
Furthermore, whence do such activities derive their budgetary legitimacy?